The invention relates to improvements in torque applying or torquing tools, namely to tools which can be used to apply a predetermined torque to bolts, nuts and analogous components having a non-circular torque-receiving part. Typical examples of such torque-receiving parts are the heads of bolts and the facetted external surfaces of nuts.
It is often desirable or necessary to apply a predetermined torque to a bolt, nut or an analogous component in order to reduce the likelihood or danger of damage or injury. For example, the bolt or bolts which are used to tighten the straps of hose clamps under the hood of a motor vehicle must be tightened with a certain force to prevent the escape of fuel, combustion products or other flowable media. This can be achieved by resorting to a torque wrench which is provided with a calibrated torque rod or another suitable torque monitoring and indicating device and can be manipulated by hand or by a motor. Torque wrenches are expensive and are often not available to a person who wishes to apply a selected torque to a nut, a bolt or a like rotary component.
Published French patent application No. 2 378 969 of Etablissements Caillau proposes to provide the head of a bolt in a hose clamp with a weakened central portion between two polygonal portions one of which is integral with the shank of the bolt and the other of which can be rotated by a wrench or the like. When the one polygonal portion encounters a predetermined resistance to rotation while the other polygonal portion is rotated by a wrench or the like, the central portion breaks and this indicates to the operator that a predetermined torque has been applied to the bolt. A drawback of the just described bolt is that it is not a serially produced staple article. Moreover, the broken central portion is subject to corrosion and exhibits sharp portions which are likely to injure the hand of an operator.
U.S. Pat. No. 3,331,267 to Tietge discloses a two-piece torquing tool including a sleeve having a polygonal internal surface to be placed around the external surface of a nut or around the head of a bolt, and a polygonal plug. The plug has a first portion which is received in the sleeve, a second portion which can be engaged by a wrench to rotate the sleeve and the nut or the bolthead which is surrounded by the sleeve, and a weakened third portion between the first and second portions. The third portion breaks when the component which is being rotated by the sleeve begins to offer a certain resistance to further rotation. This torquing tool exhibits the same drawbacks as that of Caillau and is even more expensive because it must be assembled of two parts neither of which is a serially produced staple article capable of being put to other uses in the same way as a standard screw or bolt.
Other types of breakable torquing tools are disclosed in French Utility Model No. 2 560 100 of Manier and in published German patent application No. 29 41 438 of Kesselman. All of the above described conventional torquing tools exhibit the drawback that a portion of the tool breaks away or that the tool is ripped open when the component which is being rotated begins to exhibit a predetermined resistance to further rotation. Thus, at least a portion of the tool becomes separated from the component which has been rotated and such portion is likely to fall into a machine where it can cause damage (e.g., under the hood of a motor vehicle). Once the tool is separated from the component to which a predetermined torque was applied, an inspection of the component cannot reveal whether or not a predetermined torque has been applied thereto (unless the person in charge uses a torque wrench with a graduated scale to indicate the resistance which the component offers to any further rotation. Still further, a once used conventional tool must be discarded since an essential part has been sheared off or the entire tool was ripped open to thus prevent any renewed use.